As the design rule for a semiconductor device, such as a DRAM (dynamic random access memory) has been gradually reduced, the circuit configuration in the peripheral region becomes more important.
In the case of circuits provided in the peripheral region, many capacitors, such as a pumping capacitor or a reservoir capacitor, are necessary for the purpose of charge pumping or voltage stabilization of a power line.
An embedded memory cell typically includes an access transistor and a capacitor.
The capacitor of a memory cell can have a MOS (metal oxide semiconductor) capacitor structure formed on a trench insulating region. In order to form the MOS capacitor structure, a planarization process is performed after filling a trench of a substrate with insulating material(s). The insulating material(s) filled in the trench is partially etched by using a photo mask, and then a polysilicon layer forming a capacitor field plate is formed on the substrate such that the trench having the partially etched insulating material(s) is filled with the polysilicon layer.
At this time, the insulating material remaining in the trench has the function of spacing a cell region such that charges at opposite sides of the trench can be isolated from each other, and the polysilicon layer formed over the whole area of the substrate and in the trench may enable the operation of the mass-storage capacitor.
However, when the insulating materials filled in the trench are etched to define the capacitor field plate, it is difficult to adjust the etching rate between the inside of the trench and the insulating layer formed on the substrate due to various process parameters. Also, there is a difference of the etching region for each unit cell, so the isolation characteristic is lowered and the capacitance is reduced.
In addition, even if the capacitor is formed with the above trench structure, there is limitation of utilizing trench surfaces that determine the capacitance of the capacitor, so a highly integrated mass-storage capacitor may not be obtained.